Multiple-input and multiple-output (MIMO) techniques have been an important area of focus for next-generation wireless communication systems because they can provide high capacity, extended coverage, increased diversity, and/or interference suppression. For applications such as wireless local area networks (LANs) and 4G cellular networks, MIMO systems are sometimes deployed in environments where a single access point (AP) or base station (BS) communicates with many users simultaneously, concurrently, and/or contemporaneously. As a result, multi-user MIMO has emerged as an important feature of next-generation wireless networks. This feature has the potential to combine the high capacity of MIMO processing with the benefits of space-division multiple access (SDMA).
In multi-user (MU) wireless communications, different users (e.g., receivers/stations) are to be served with various qualities of service (QoS) requirements. When multiple antennas are used at the user transmitter and/or receiver, they can provide multiple access gain by spatially separating the signals to different users. Therefore, the multiplexing and scheduling methods implemented by MIMO transmitters play a role in determining the communication system capacity in a multi-user MIMO environment because different users can be assigned various data transmission rates with respect to their instantaneous channel status information (CSI), buffer backlogs, transmit (Tx)/receive (Rx) antennas, and MIMO processing techniques. These scheduling methodologies are especially attractive for 4G cellular systems and wireless LANs as they provide high data rates in addition to supporting multiple classes of services with various QoS requirements.
However, there is a need for efficient scheduling and/or transmission methods to improve MIMO transmissions.